The Effect of Solution Concentration on the Electrochemical Behaviour of AISI 321 Stainless Steel in Sulfuric Solutions

The semiconductor properties of passive films formed on AISI 321 stainless steel (AISI 321) in six acidic solutions under open circuit potential (OCP) conditions were evaluated by potentiodynamic polarization, Mott– Schottky analysis and electrochemical impedance spectroscopy (EIS). Mott–Schottky analysis revealed that the passive films behaved as n-type and p-type semiconductors at potentials below and above the flat band potential, respectively. Also, Mott–Schottky analysis indicated that the donor and acceptor densities were in the range 1021 cm-3 and increased with solution concentration. EIS data also showed that the display of Nyquist plots, and hence the mechanism of corrosion, depended on the acid concentration. In 0.005, 0.010 and 0.050 M concentration, the equivalent circuits Rs(RctQdl) described the corrosion systems. However, at concentrations ? 0.100 M, the equivalent circuit Rs(Qdl[Rct(RrQr)]) by two time constants was applicable.